The debate over how long it will take before disposable incomes start rising again has been stoked further after a respected thinktank argued that the average family will be forced to wait until next year.

The Resolution Foundation said an in-depth review of household incomes found they will begin to rise above inflation in 2015 – after a five-year wait. However, the living standard of the average household in 2018 will still be 3.5% lower than in 2008, the thinktank added.

The Resolution Foundation said a detailed assessment of living standards in Britain found that an increase in disposable incomes next year will be "barely positive" and will be no more than 1% a year for each of the following three years. The report contradicted a Treasury study that said disposable incomes started improving in 2012/13.

"The living standards of the typical household will still be 3.5% lower in 2018-19 than they were at the start of the financial crisis of 2008, only just inching above the level they were last at in 2005-06," said the thinktank.

The report, The State of Living Standards, paints a contrasting picture of family incomes to the one put forward by George Osborne last month. Citing research by the Treasury, the chancellor said that tax relief from a higher personal allowance had pushed up disposable incomes in the 2012/13 financial year, offsetting depressed wages and rising prices, especially gas and electricity hikes.

Treasury officials came under fire for excluding cuts in tax credits and benefits from their sums and ignoring a trend since last spring of falling wages.Gavin Kelly, the thinktank's chief executive, said: "Our evidence suggests that the fall in living standards is bottoming out and should start to rise again next year. That's the good news and given year after year of decline it will come as a relief. But as things stand the recovery for families looks like being painfully slow – by 2018 we expect the typical household to still be worse off than they were before the crisis."

Meanwhile, a report by the business lobby group the CBI said that business were already investing to take advantage of the upturn in the UK's fortunes. In its quarterly report on the state of the world economy, it found that British businesses had commissioned new IT systems, machinery and raised their marketing budgets to take advantage of GDP growth that ranks alongside the US as the best among western economies.

Growth this year will reach 2.6%, up from the previous forecast of 2.4% boosted by a turnaround in business investment from -3.7% last year to 6.6% this year.

However, the political uncertainty created by the Scottish referendum, a hard-fought general election in 2015 and the possibility of an in-out EU referendum could persuade businesses to delay investment plans, it said.

The CBI's policy director, Katja Hall, said: "Political risks are at the top of the agenda for lots of businesses and especially those based outside the UK that are considering large investments."

Over the last year the economy has relied on consumers to maintain the recovery and January was no different, according to the latest figures from the British Retail Consortium (BRC). Discounts on furniture and household goods pushed retail sales 5.4% higher last month, compared with January 2013.

But the BRC warned that the figures were distorted by a sharp fall in sales last January and pointed to the more modest 1.7% quarterly comparison.